1. Field of the Invention
The present invention generally relates to facsimile machines, and more particularly to a facsimile machine including a data access arrangement (DAA) in the form of a semiconductor device (hereinafter referred to as a semiconductor DAA) and having an automatic switching function from telephone to facsimile (hereinafter also referred to as TEL→FAX) based on detection of a calling tone signal. (CNG signal), a facsimile communication network service function based on detection of a facsimile communication network signal (FCC signal), and a TEL→FAX remote switching function based on detection of a dual tone multi-frequency signal (DTMF signal).
2. Description of the Related Art
The conventional facsimile machine as disclosed in Japanese Laid-Open Patent Application No. 5-122428 or No. 8-139886, in order to establish interface (I/F) with a telephone line (line I/F), employs two transformers: one terminated by 600 Ω for impedance consistency between a FAX modem and the telephone line and for insulation between an integrated circuit on the network side and an integrated circuit on the modem side, and the other terminated by high impedance for transmission and insulation between the integrated circuit on the network side and the integrated circuit on the modem side with respect to the CNG signal, the FCC signal, and the DTMF signal that are tone signals.
On the other hand, recently, the semiconductor DAA, which realizes the analog circuit of the line I/F in the form of a semiconductor device without using transformers, has been used as an interface for a data modem, thus realizing circuit simplification and reduction in circuit size and cost.
The semiconductor DAA (hereinafter referred to as a silicon DAA) may be used in a facsimile machine as shown in FIG. 1. In FIG. 1, a line I/F part 11 is established between a network 2 and a modem 12. The line I/F part 11 includes the silicon DAA, that is, an integrated circuit 113 on the network side, a reception and transmission part 114, and an integrated circuit 115 on the modem and main control part side. The line I/F part 11 further includes a CML (Connect MODEM to Line) relay 110, a diode bridge (full-wave rectifier circuit) 111, a hook switch 112, and a hook detector circuit 116.
In the case of using the silicon DAA in the facsimile machine, it is additionally required to perform-detection of the CNG signal as the TEL→FAX automatic switching function, detection of the FCC signal as a call signal in the FAX communication network service, and detection of the DTMF signal as the TEL→FAX remote switching function. The silicon DAA, however, does not include a part receiving and transmitting these tone signals. Therefore, it is required, as conventionally, to provide a transformer 118 terminated by high impedance outside the silicon DAA.